package com.zxlfysj.floyd;

import java.util.Arrays;

/**
 * 弗洛伊德算法实例
 *
 * @author yangshujing
 * @create 2020-08-26 21:15
 */
public class FloydAlgorithm {
    public static void main(String[] args) {
        char[] vertex = {'A', 'B', 'C', 'D', 'E', 'F', 'G'};
        //创建邻接矩阵
        int[][] matrix = new int[vertex.length][vertex.length];
        final int N = 65535;
        matrix[0] = new int[]{0, 5, 7, N, N, N, 2};
        matrix[1] = new int[]{5, 0, N, 9, N, N, 3};
        matrix[2] = new int[]{7, N, 0, N, 8, N, N};
        matrix[3] = new int[]{N, 9, N, 0, N, 4, N};
        matrix[4] = new int[]{N, N, 8, N, 0, 5, 4};
        matrix[5] = new int[]{N, N, N, 4, 5, 0, 6};
        matrix[6] = new int[]{2, 3, N, N, 4, 6, 0};

        Graph graph = new Graph(vertex.length, matrix, vertex);
        graph.floyd();
        graph.show();


    }
}

//创建图
class Graph {
    private char[] vertex; //顶点数组
    private int[][] dis; // 顶点到顶点的距离，存放最后结果
    private int[][] pre; //保存到目标顶点的前驱顶点（中间顶点）

    public Graph(int length, int[][] matrix, char[] vertex) {
        this.vertex = vertex;
        this.dis = matrix;
        this.pre = new int[length][length];
        for (int i = 0; i < length; i++) {
            Arrays.fill(pre[i], i);
        }
    }

    //显示结果
    public void show() {
        for (int k = 0; k < dis.length; k++) {
            for (int i = 0; i < dis.length; i++) {
                System.out.print(vertex[pre[k][i]] + " ");
            }

            for (int i = 0; i < dis.length; i++) {
                System.out.print("(" + vertex[k] + "到" + vertex[i] + "最短路径为" + dis[k][i] + ")");
            }
            System.out.println();
        }
    }

    public void floyd() {
        int len = 0;
        for(int k = 0; k < dis.length; k++) { //k为中间顶点的坐标
            for(int i = 0; i < dis.length; i++) { //从i顶点出发
                for(int j = 0; j < dis.length; j++) {  //到终点顶点j
                    len = dis[i][k] + dis[k][j];
                    if(len < dis[i][j]) { //即i和j经过中间顶点K的比i、j直连的短
                        dis[i][j] = len; //更新距离
                        pre[i][j] = pre[k][j]; //更新前驱顶点
                    }
                }
            }
        }
    }
}
